A building typically has a load center or “breaker box” that distributes power from a primary power supply, such as a utility power supply, to various circuits within the building. The load center generally includes a main breaker, which selectively connects/disconnects the individual circuits or branches of the load center to/from the primary power supply. Increasingly, transfer panels or switches are being used so that critical or emergency circuits, such as those that feed power to water and waste management systems, refrigeration systems, and medical equipment, are sufficiently powered during interruption or failure of the primary power supply. The transfer panel, similar to the load center, will include individual circuits that are connected to the primary power supply through a transfer switch, similar in operation to the main breaker of the load center. During normal operation of the primary power supply, primary power is delivered to the circuits of the load center and the transfer panel. However, during interruption of primary power, the transfer switch disconnects the circuits of the transfer panel from the primary power supply and connects those circuits to an auxiliary power supply, such as an electric power generator.
Transfer switches are generally categorized as either manual transfer switches or automatic transfer switches. Automatic transfer switches automatically detect the interruption of primary power, automatically connect the critical or emergency circuits to the auxiliary power supply, and automatically initiate operation of the auxiliary power supply. Moreover, automatic transfer switches will automatically restore connection of the critical or emergency circuits to the primary power supply when primary power is restored and shut-down the auxiliary power supply. With manual transfer switches, the aforementioned steps are carried out manually by an operator.
Specifically, upon interruption of primary power, the main breaker must be manually disconnected or turned “OFF’ and the circuits connected to the auxiliary power supply. The main breaker is disconnected to prevent power generated by the auxiliary power supply from back-feeding through to the primary power supply. Thus, even when primary power has been restored, the load center remains disconnected from the primary power supply. As a result, the user, e.g., homeowner, is not readily made aware that primary power has been restored and that the auxiliary power supply can thereby be turned “OFF” or shut down and the circuits of the building may be reconnected to the primary power supply. Conventionally, to determine if primary power has been restored, a user must shut down the auxiliary power supply and reconnect the load center to the primary power supply. If the load center circuits are energized, primary power has been restored. If not, the user must then manually disconnect the load center from the primary power supply and reinitiate the auxiliary power supply to provide power to the transfer switch circuits, as described above. Unless the user is ostensibly aware that primary power has been restored, this technique can be hit-and miss, and therefore considerably inefficient.
Additionally, in many applications, the auxiliary power supply is a fuel-driven generator. Thus, if auxiliary power is used to power the critical or emergency circuits notwithstanding the restoration of primary power, the fuel-driven generator may be run much longer than needed thereby increasing its operational costs.
Therefore, there is a need for a device that detects primary power delivery to a load center and provides a suitable indication to a user. Such a device is particularly needed in the context of manual transfer switches in order to provide a signal to a user that primary power has been restored, that the auxiliary power supply may be shut down, and that the load center may be reconnected to the primary power supply.